The invention relates to the field of wire cloth screen surfaces or panels useful for sorting of sand, gravel, limestone or other fragmented materials, and includes a new, high-production wire cloth screen panel and means for mounting the panel in commercially available vibratory screen boxes.
Harp screens have been known and used for a number of years to sift fragmented material and to control the size of the material passing through the screens. Such harp screens have, in the past, been extremely expensive, formed of a multiplicity of generally parallel, elongated wires without transverse spacers, and such wires have been individually mounted and tensioned in screen boxes. Typically, substantial amounts of time are required to individually mount the many elongated wires, and maintenance time required to keep such screens effective is extremely high. In order for the screen to function effectively the individual wires must be kept continually taut. Because the wires rapidly stretch and sag when used in a conventional vibrating screen box, the wires have had to be continually adjusted to maintain proper tension or the harp screen would rapidly wear out and require replacement. The high initial cost of installing such harp screens and the substantial subsequent maintenance cost and downtime have discouraged extensive use of the harp screens even though high-production levels can be achieved with their use. Accordingly, it is desirable to provide a new, improved wire cloth panel having high-production capacity but which is inexpensive and easily installed and tensioned as a unit.
One serious shortcoming of the known harp screens is that their multiplicity of parallel, spaced-apart, longitudinal wires have not been interconnected by any transverse spacers or wires, and, accordingly, unless the wires have precisely the right tension and spacing, unwanted oversized particles tend to wedge between the wires and either pass through the screen or widen the gap between wires, thereby passing larger material through the screen than that intended. This shortcoming is further compounded as the wires stretch or sag in normal usage, thus requiring maintenance downtime to correct this condition.
Maintaining the commercially available harp type screens has been extremely time consuming and expensive. Available screens have their longitudinal wires individually adjustable, and an operator must individually tighten threaded shafts or the like for each of the myriad of wires to assure that the wires have the desired tension. Proper tension is critical because when the wires begin to sag, the excessive vibration can cause flexing of the wire, resulting in metal fatigue and breakage in a matter of hours. In heavy usage, an operator must adjust and tighten harp screen wires on numerous occasions during a day's operation, and when each of several hundred wires may require adjustment and tensioning the amount of downtime and the maintenance expense can become very substantial.
Still another problem encountered with standard commercially available wire screen panels is that such panels have great difficulty in sifting and classifying material which is moist or wet. When the material is moist and contacts a screen having standard apertures, the apertures tend to clog or blind almost immediately, thus seriously limiting the productive capacity of the wire cloth panel. The same problem is encountered with materials which are hydrous or hydroscopic and tend to absorb moisture from the air. Typical of such materials is ag-lime used for soil treatment in farming, and which requires sorting so as to not exceed a predetermined size range specified by state and federal regulations. Such material is frequently used in agriculture and is much in demand.
For a number of years those skilled in the art sought solutions by which hydrous or moist materials could be processed with wire cloth screens without clogging the wire cloth apertures. Prior to the invention, one of the better known solutions has been to utilize special electric heating equipment to heat the wire cloth panel itself to dry the wire, preventing the material from clinging to the wire panel and creating a blinding or clogging effect over the wire cloth apertures. While this technique has produced limited success, the cost of electrical heating devices and their installation is in the thousands of dollars, and immense amounts of electrical energy are required to keep the systems operating. Naturally, it would be desirable to provide an improved wire cloth screen panel which successfully handles moist or hydrous materials without clogging and without the need for electrical high-output heaters or the expenditure of great amounts of heat energy.
Accordingly, it would be highly desirable to provide a new and improved wire cloth screen surface or panel capable of rapidly sorting large quantities of fragmented material even when moist or hydrous in nature, a screen which is easily installed and maintained, and one which requires no heaters or electrical heat energy to operate. The present invention accomplishes these goals.